The present invention pertains generally to the control of internal combustion engines where the speed of a first engine is synchronized with some reference speed such as the speed of a second engine, particularly as found in twin engine boats having independent manual throttle controls.
Recently, a number of very accurate electronic synchronization indicators have come on the market with the claim that the operator can synchronize the engines by adjusting the manual controls while observing the indicator. Typically, however, manual controls cause a change in speed of nearly two thousand rpm per inch of travel, are connected to the throttles by long flexible cables (or linkages), and have external springs to reduce lash, so that synchronization by this method is a tedious course-adjustment at best, and the springs tend to urge the vibrating controls away from synchronization once set. An additional apparatus is clearly needed, yet prior apparatus designed to synchronize engine speeds under cruising conditions invariably interfere with the independent manual control needed for certain maneuvers. In panic conditions, the operator may not remember or have enough time to disengage the appratus, reengage linkage members, or lock down moving levers. Therefore, special overriding lever arrangements and resilient couplings were added to these apparatus so that the operator could overpower the apparatus by forcibly holding friction drives and clutches in a slip condition. Invariably this forced slippage wore out the parts and increased maintenance costs. Consequently, other devices to protect the apparatus were added such as solenoids, limit switches, ratchet wheels, etc., which only increased the complexity and production costs, but decreased reliability by their very presence. It is the solution of these problems to which the present invention is directed.